Office chairs have been developed which permit the back to be tilted synchronously with the seat but at a greater rate so that the back tilts relative to the seat as the latter tilts relative to the chair base. Such chairs commonly incorporate what is often referred to as a synchrotilt control mechanism so as to permit the simultaneous but differential rearward tilting of the seat and back away from the normal upright position, with this differential tilting of the back and seat typically being in the ratio of about 2 to 1. Many of these mechanisms provide a pivot or tilt axis in the vicinity of the front edge of the seat to prevent undesired lifting of the seat front edge when the occupant tilts the chair rearwardly away from the normal upright position. In addition to these conventional rearward tilting movements, many chairs have also been developed which enable the seat to effectively pivot forwardly from the normal upright position, that is, the seat can be made to assume a position wherein it slopes downwardly in a forward direction so that the rear of the seat is at an elevation above the front of the seat. This forward tilt feature on the seat has been found to be highly desirable in many of the more intensive work environments such as when the chair occupant is working on a keyboard or doing intensive paperwork on a worksurface such as a desk or table. The incorporation of this forward seat tilt feature into chairs provided with a control mechanism which provides synchronous differential rearward tilting of the seat and back, however, has created additional complications which in many chairs have not been satisfactorily resolved.
For example, in known synchrotilt chairs wherein a forward seat tilt feature has been incorporated in addition to the synchronous differential rearward tilting of the seat and back, the synchronous differential tilting relationship between the seat and back continues to function irrespective of whether the seat and back are being tilted forwardly or rearwardly from the normal upright position. Hence, while this provides for satisfactory performance during rearward tilting from the normal upright position since the angle between the seat and back increases during such rearward tilting, nevertheless the functional performance of this mechanism during forward tilting is undesirable since the angle between the seat and back decreases as the seat and back are tilted forwardly from the normal upright position. This closure of the angle between the seat and back during forward tilt thus causes the chair to be uncomfortable and severely restricts the occupant's satisfactory use of the chair when in the forward tilt position.
To overcome the aforementioned problem and disadvantage, one known chair which incorporates a synchrotilt mechanism for permitting synchronous differential rearward tilting of the seat and back has been provided with a mechanism which permits only the seat to undergo forward tilt. With this arrangement, the angle between the seat and back thus increases when the seat is in the forward tilt position in comparison to the normal upright position. This positioning of the back, however, is undesirable when the occupant is carrying out intensive work on a table or desk, such as writing and the like, since under such work conditions an occupant often wishes to sit on the forwardly inclined seat in a forwardly leaning position, and in such case the back of the chair, being in the stationary upright position, is not disposed for supportive engagement with the occupant's back.
In another chair which has been developed to provide both rearward and forward tilt, only the back is permitted to tilt rearwardly under normal chair usage. While the seat and back can be tilted forwardly as a unit, this requires two separate actuators for controlling forward tilt and tilt locking. This known chair also does not provide advantageous synchronous differential rear tilting.
Still another disadvantage associated with many of the known chairs which have attempted to provide both rearward and forward tilt capabilities is the number of control arms or buttons which must be activated by the chair occupant in order to move the chair into a forward tilt position. In many such chairs it has been observed that the occupant must often activate two or more lever arms, buttons or control knobs before the chair can be forwardly tilted, and such complex control makes use of the chair confusing and difficult since in such cases it has been observed that the chair may possess as many as four different actuators positioned under the chair seat so as to control the various chair functions, and this large number of actuators is often confusing to the chair occupant, particularly in those situations where the chair is not one which is used on a high intensity basis by solely the same occupant.
Accordingly, it is an object of this invention to provide an improved chair which provides for synchronous differential rearward tilting of the seat and back away from the normal upright position, and which improved chair in addition permits forward tilting of the seat and back away from the upright position, which forward tilting occurs with the differential synchronous movement disabled so that the seat and back effectively tilt forwardly as a unit so as to maintain a substantially constant angle between the seat and back.
More specifically, according to one aspect of the invention, the improved chair, as aforesaid, incorporates a synchronous tilt control mechanism which connects the chair base to the seat and back to permit rearward synchronous differential tilting thereof away from the normal upright positions, with this synchronous tilt control mechanism also incorporating a control linkage which can be adjusted between forward and rearward tilt positions so that, when in the forward tilt position, the differential synchronous relationship is disabled, and the seat and back will thus tilt forwardly away from the upright position without causing any significant differential tilting between the seat and back.
A further aspect of the invention is an improved chair, as aforesaid, wherein the linkage which disables the differential synchronous tilting relationship is activated by a single occupant-engaged control arm or element disposed in the vicinity of the underside of the chair so as to provide for simple occupant control over forward tilt when such forward tilt is desired.
A still further aspect of the invention is an improved chair, as aforesaid, wherein the single control which disables the differential synchrotilt linkage to permit forward tilt also automatically activates a multi-position lock device so that as the seat and back assemblies are tilted forwardly as a unit, the lock device will automatically maintain the seat and back in the forwardly tilted position, depending upon the angle through which forward tilt occurs.
Still a further aspect of the invention in an improved chair, particularly a chair having both forward and rearward tilt capabilities as aforesaid, having an improved seat assembly whereby the seat assembly includes a seat support member which is movably supported on the chair control, and which seat support member in turn mounts thereon the seat, which seat can be slidably displaced along the seat support member in the front-to-back direction and selectively locked by the occupant in a desired position by the occupant so as to provide the occupant with improved seating comfort by permitting selection of seat position relative to the back. This seat assembly particularly employs constructional features which facilitate the economical manufacture and assembly thereof.
Other objects and purposes of the invention will be apparent to persons familiar with chairs of this general type upon reading the following specification and inspecting the accompanying drawings.